What is Private Constructor in C#

When we do not want objects to be created of a class we can declare private constructors

A private constructor is simply an instance constructor of a class which is declared to be 'private' and so can't be accessed directly by code outside the class.

As regards its uses, please check this recent thread:

http://www.c-sharpcorner.com/Forums/Thread/176868/advantage-of-private-constructor-in-C-Sharp.aspx